Low blood sugar, called hypoglycemia, happens when your blood glucose drops below 70 mg/dL. The most common causes include skipping meals, drinking alcohol without eating, certain medications, and exercising more than usual. If you don’t have diabetes, low blood sugar is less common but still possible, and it points to something specific your body is doing (or failing to do) with glucose.
How Your Body Normally Keeps Blood Sugar Stable
Your body runs a tightly controlled system to keep blood sugar in a narrow range. When levels start to dip, your pancreas releases a hormone called glucagon that signals your liver to convert its stored glucose into a usable form and release it into your bloodstream. Your liver can also build new glucose from proteins and fats when stores run low, a process that kicks in during prolonged fasting. When this system works properly, your blood sugar stays steady even between meals or overnight.
Low blood sugar means something disrupted that process. Either your body used glucose faster than it could be replaced, your liver couldn’t release enough, or too much insulin pushed your levels down. The specific reason depends on your situation.
Common Causes if You Have Diabetes
For people taking insulin or certain diabetes medications, low blood sugar is a well-known side effect. It typically happens when you take your usual dose but eat less than expected, skip a meal, or exercise harder than normal. The medication lowers your blood sugar as designed, but without enough food to balance it out, levels drop too far. Timing matters too: some insulin types peak hours after injection, which is why blood sugar can fall in the middle of the night even if dinner felt like enough.
Common Causes Without Diabetes
If you don’t take diabetes medications, low blood sugar is less likely but still has clear explanations. The main categories are reactive hypoglycemia (after eating) and fasting hypoglycemia (between meals or overnight).
Reactive Hypoglycemia
This happens within four hours after a meal, most often after eating a large amount of carbohydrates. Your body overproduces insulin in response to the sugar spike, which then drives blood glucose too low. Some people experience symptoms like shakiness and brain fog after high-carb meals but never actually measure low glucose. Doctors call this “postprandial syndrome,” and while it feels identical to true hypoglycemia, it’s a distinct pattern where symptoms occur without blood sugar actually dropping below 70 mg/dL.
Skipping Meals or Not Eating Enough
Your liver stores a limited supply of glucose. If you go long stretches without eating, those stores get used up and your body has to manufacture glucose from other sources, which is slower and less efficient. Prolonged fasting, very low calorie diets, and eating disorders like anorexia can all deplete those reserves enough to cause hypoglycemia.
Alcohol
Drinking on an empty stomach is one of the most common non-diabetes causes. Alcohol directly interferes with your liver’s ability to produce new glucose. Research shows that gluconeogenesis (your liver’s process of making fresh glucose) drops by about 45% in the five hours after drinking, and the raw materials your liver needs for that process fall by roughly 61%. Your liver is so busy processing alcohol that it can’t do its other job of keeping your blood sugar stable. This is why heavy drinking without food is particularly risky.
Medications
Several drugs not designed for diabetes can lower blood sugar as a side effect. These include certain antibiotics used to treat infections, the antimalarial drug quinine, and accidentally taking someone else’s diabetes medication. People with kidney problems are especially vulnerable because their bodies can’t clear medications as efficiently, allowing drugs to build up and have a stronger effect on glucose levels.
Medical Conditions That Cause Low Blood Sugar
Sometimes low blood sugar signals an underlying health problem. Severe liver disease, including hepatitis and cirrhosis, limits the liver’s ability to store and release glucose. Advanced kidney disease and serious heart disease can also cause it. These are typically conditions you’d already know about, not something that shows up as a surprise.
Hormonal problems are another category. Your adrenal glands produce cortisol, which helps maintain blood sugar between meals. When these glands don’t produce enough cortisol (a condition called adrenal insufficiency), your blood sugar can drop, particularly during illness, fever, or periods of stress. A related issue involves the pituitary gland in the brain, which controls the adrenal glands. Pituitary problems that reduce cortisol production are actually more likely to cause hypoglycemia than primary adrenal disease. Cortisol also plays a role in producing adrenaline, so people with adrenal insufficiency have lower adrenaline levels, which means their bodies are less equipped to mount the normal “fight back” response when blood sugar falls.
Rarely, a tumor on the pancreas called an insulinoma can produce excess insulin and cause repeated episodes of low blood sugar. This is uncommon but worth investigating if you have frequent unexplained episodes.
Recognizing the Symptoms
Low blood sugar produces two distinct waves of symptoms, depending on how far your levels have dropped.
The first wave is your body’s adrenaline response: sweating, shakiness, a fast heartbeat, anxiety, and sudden hunger. These are your early warning signs, and they’re your body’s way of alerting you that something needs to change. Most people notice these when glucose is below 70 mg/dL but still above 54 mg/dL.
If blood sugar continues to fall, brain-related symptoms take over. Your brain depends almost entirely on glucose for fuel, so it’s the first organ to struggle. This second wave includes weakness, dizziness, difficulty concentrating, confusion, blurred vision, and behavior that can look like intoxication. Below 54 mg/dL is considered severe hypoglycemia. In extreme cases, it can lead to seizures or loss of consciousness.
What to Do When Blood Sugar Drops
The standard approach is called the 15-15 rule: eat or drink 15 grams of fast-acting carbohydrates, wait 15 minutes, then check your blood sugar again. If it’s still below 70 mg/dL, repeat the process. Good options for 15 grams of quick carbs include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey. Young children need less than 15 grams per round.
Once your blood sugar is back in a normal range, eat a small meal or snack that includes some protein or fat to keep it stable. If someone loses consciousness from severe low blood sugar, they need an emergency glucagon injection, which rapidly signals the liver to dump stored glucose into the bloodstream.
Low Blood Sugar During Sleep
Nocturnal hypoglycemia is harder to catch because you’re not awake to notice the early symptoms. Common causes include skipping dinner, exercising in the evening, and drinking alcohol before bed. Signs that it happened overnight include waking up with a headache, feeling unusually tired, or finding your sheets damp from sweating.
If you suspect this is happening, options include setting an alarm to check your blood sugar in the early morning hours, or using a continuous glucose monitor that checks levels every five minutes and sounds an alarm when they drop too low. Adjusting when and what you eat in the evening can also help: a bedtime snack with both carbohydrates and protein gives your body a slower, steadier fuel source through the night.
When Low Blood Sugar Keeps Happening
A single episode after skipping lunch or drinking on an empty stomach is easy to explain. Repeated episodes without an obvious trigger are different. If you’re frequently experiencing symptoms of low blood sugar, especially if they’re happening while fasting or waking you at night, that pattern warrants blood work to check for hormonal imbalances, liver or kidney function issues, or excess insulin production. Keeping a log of when episodes happen, what you ate beforehand, and what your blood sugar reads (if you’re able to check) gives your doctor the most useful information to work with.